Rett Syndrome (RTT), a neurodevelopmental disease in the family of Autism Spectrum Disorders, is caused by defects in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2), affecting one in every 10,000 live births of females. RTT patients show breathing abnormalities such as episodic respiratory irregularity, breath-holding, apnea, hyperpnea, apneusis, Valsalva breathing, air swallowing, etc. The breathing disorders play a role in the sudden unexplained death and contribute to the abnormal development of the brain. Most of the breathing disturbances are recapitulated in Mecp2- knockout mice in which defects in brainstem respiratory neuronal activity, neurotransmitter systems, protein expression and brain-derived neurotrophic factor have been shown to play a role. Another potential mechanism for the breathing disorders is central CO2 chemoreception (CCR) serving for the feedback regulation of respiratory activity, as disruption of the CCR can lead to severe breathing consequences. Our preliminary studies indicated that the breathing response to a particular level of hypercapnia was impaired in male hemizygous Mecp2-knockout (Mecp2-/Y) mice, accompanying with defects in the several candidate proteins for CO2 chemosensitivity and catecholamine biosynthesis. The CCR defect occurred during maturation and was not seen at age of 4 weeks. We believe that these are important findings, as a novel etiology for the respiratory dysfunction is suggested in the mouse model of RTT. Since the CCR disruption and breathing arrhythmias occur at certain age after birth, detailed studies of the development of the CCR disruption and its molecular and cellular basis may shed insight into the disease and help to formulate effective therapeutic modalities to control breathing disorders in RTT patients. Therefore, we have proposed experiments to address following specific aims: 1) to demonstrate the CCR disruption and its developmental course in Mecp2-/Y mice, and 2) to determine the cellular and molecular abnormalities associated with the development of CCR disruption in Mecp2-/Y mice. Outcome of the studies will advance the understanding of RTT and the design of effective therapeutic modalities to alleviate symptoms and prevent unexpected death of RTT patients. PUBLIC HEALTH RELEVANCE: Rett Syndrome is a neurodevelopmental disease in the Autism Spectrum Disorders. Rett patients show breathing disorders for some unknown reasons, which we hypothesize to be related to the disruption of brainstem CO2 chemoreception. Studies on the development of breathing disorders will lead to information to alleviate breathing disorders and reduce the sudden and unexpected death of the disease.